Reinforced tubular joint for improved sealing-tightness after plastic expansion

ABSTRACT

The invention relates to a high-performance threaded tubular joint comprising a first, male tubular element ( 11 ) and a second, female tubular element ( 12 ) made up together by screwing. One of the tubular elements ( 11; 12 ) has a non-threaded lip ( 38; 5 ) extending between its thread and its free end and having a sealing surface ( 40; 7 ) in sealing-tight contact with the opposite surface ( 41; 8 ) of the other element after screwing together, diametric expansion, and then generation of springback forces of the first and second tubular elements. The joint has a tubular sleeve ( 34; 36 ) threaded over the second element ( 12 ) before screwing together and positioned to extend axially substantially opposite to the lip ( 3; 5 ) and, after diametric expansion, generating a springback force which is added to that of the second element in order to counteract the springback force of the first element, thus effecting at least the shrink-fitting of the tubular sleeve over the second element.

The invention relates to a tubular joint, in particular of the type usedfor hydrocarbon wells or similar wells, e.g. in the field ofgeothermics.

Such a joint may exist between two great-length tubes or between agreat-length tube and a coupling. These joints are used in particularfor assembling strings of casings or tubings. Taking into account themechanical features required, the casings and tubings are generally madeof heat-treated steel.

For their part, the joints must withstand tension, compression, bendingand sometimes twisting as well as widely differing pressure in bothdirections between the inside and the outside. Furthermore, they musteven be gas-tight, at least in certain cases. Threaded joints areparticularly advantageous in this respect.

However, it is currently intended to subject the tubes in situ todiametric expansion with permanent plastic deformation. This has variousadvantages, which will be referred to below. Again it is necessary thatthe joints remain operational after the plastic deformation due todiametric expansion to which they are subjected like the tubes. Thus itis desirable that the threaded joints hold after plastic diametricexpansion whilst substantially retaining the features for which they arevalued, in particular mechanical strength under tension/compression,with or without internal or external high pressure, as well assealing-tightness. A joint remains sealing-tight at liquid and/or gaspressures which are even greater if the contact pressure between theparts of the joint is strong over a good width and over the entireperiphery of the surfaces in contact.

Conventional joints are not entirely satisfactory: either they do notmeet these requirements, or they meet them in a random manner, or theymeet them but not repeatedly.

In WO 02/01102, a joint structure is proposed intended to withstandplastic diametric expansion. In FR 02 00055, the Applicant has likewiseproposed an improved joint structure to withstand plastic diametricexpansion.

The present invention has just improved the situation and moreparticularly the sealing-tightness of the threaded joint.

The invention relates to a high-performance threaded tubular jointcomprising a first, male tubular element and a second, female tubularelement capable of being made up by the screwing together of respectivemating threads. One at least of the first and second tubular elementshas a non-threaded lip extending between its thread and its free end andhaving a sealing surface capable of being in sealing-tight contact withthe opposite surface of the other element after screwing together anddiametric expansion, followed by the generation of springback forces ofthe first and second tubular elements.

According to a main feature, the tubular joint has a tubular sleevecapable of being threaded over the second element before screwing, ofbeing positioned so as to extend axially substantially opposite the lipand, after diametric expansion, of generating a springback force whichis added to that of the second element to counteract the springbackforce of the first element, thus effecting at least the shrink-fittingof the tubular sleeve over the second element.

According to an advantageous embodiment, the non-threaded lip of thefirst element has a tongue at its end capable of engaging in abutment ina corresponding groove of the second element after screwing together andbefore expansion. The non-threaded lip is also capable of being held bythe tongue in the groove during diametric expansion.

Advantageously, the sealing surface of the lip and the opposite surfaceare cylindrical and are disposed with slight clearance from one anotherafter screwing and before diametric expansion.

According to another embodiment, the sealing face of the lip and theopposite face are capable of interfering radially with one another afterscrewing together and before diametric expansion.

According to a first modified embodiment, each of the first and secondtubular elements comprises a non-threaded lip extending between itsthread and its free end and having a sealing surface capable of being insealing-tight contact with the opposite surface of the other elementafter screwing together and diametric expansion followed by thegeneration of springback forces of the first and second tubularelements. In this embodiment, the tubular joint comprises two tubularsleeves capable of being threaded over the second element beforescrewing together, of being positioned so as to extend axiallysubstantially opposite to the lips respectively, and of generating aspringback force which is added to that of the second element tocounteract the springback force of the first element, thus effecting atleast the shrink-fitting of the tubular sleeve over the second element.

In a second modified embodiment, the two sleeves are connected togetherby a brace having a cross-section smaller than that of the sleeves, thesleeves and the brace being formed in one piece.

Advantageously, the tubular brace has a radial thickness less than thatof the sleeves.

According to one embodiment of the invention, each tubular sleeve has anoverlap length roughly equal to the length of the opposite lipoptionally with the addition of a length corresponding to at most 8times the pitch of the threads.

Advantageously, each sleeve is centred over the opposite lip.

In an advantageous embodiment, the tubular sleeve extending opposite tothe lip of the second element has a radial projection capable of cominginto contact with a radial surface located at the end of the secondelement and capable of facilitating positioning of the tubular sleeve.

Preferably, the tubular sleeve is kept in position relative to thesecond element by adhesion of at least part of the surfaces of thesecond element and of the opposite sleeve.

The tubular sleeve is positioned axially on the second element by meansof shrink-fitting at least by cooling of the second element and/orheating of the tubular sleeve.

In order to facilitate positioning of the tubular sleeve, the secondelement has a mark located on its outer peripheral face. In a possibleembodiment, the mark is a shallow groove formed on the second element.

Preferably, the radial thickness of the tubular sleeve is at least equalto 1.5 mm.

The material of the tubular sleeve has a yield strength higher than theyield strength limit of the material of the first and second elements.Moreover, the yield strength of the tubular sleeve is adjusted by heattreatment.

The invention also relates to a method of producing a sealing-tighttubular threaded joint, starting from a tubular threaded joint known asan “initial tubular threaded joint”. This initial threaded joint issubjected to diametric expansion in the region of plastic deformation bymeans of an expansion ball of a diameter greater than the inner diameterof the tubular elements, which is moved axially in the threaded joint inthe region where each sleeve generates, after expansion, a springbackforce which is added to that of the second element in the regionoverlapped by the sleeve.

The invention also relates to a high-performance sealing-tight tubularjoint, such as can be obtained by the method according to the invention,comprising a first, male tubular element and a second, female tubularelement made up by the screwing together of respective mating threads.One at least of the first and second tubular elements has a non-threadedlip extending between its thread and its free end and having a sealingsurface in sealing-tight contact with the opposite surface of the otherelement. The joint furthermore has a tubular sleeve tightly surroundingthe second element and extending axially substantially opposite to thesaid lip.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

The Figures below show in a non-limiting manner, embodiments of theinvention:

FIG. 1 shows a threaded joint of the type to which the inventionrelates,

FIG. 2, the male element of the threaded joint of FIG. 1,

FIG. 3, the female element of the threaded joint of FIG. 1,

FIGS. 4 to 7 show the threaded joint of the type to which the inventionrelates at various stages of the expansion process,

FIG. 4 shows the phase of expansion of the threaded joint,

FIG. 5, the bending phase,

FIG. 6, the straightening phase,

FIG. 7, the final state of the threaded joint after undergoing theexpansion process,

FIG. 8, a threaded joint before expansion, having an embodiment of thesleeves according to the invention,

FIG. 9, the threaded joint after expansion, having an embodiment of thesleeves according to the invention.

The drawings contain essentially elements of a certain character. Theymay therefore not only aid understanding of the description, but alsocontribute to the definition of the invention if necessary.

Annexe I shows the results of a comparative study of thesealing-tightness of a reference joint and threaded joints according tothe invention.

We refer here to the drilling of wells for hydrocarbons or geothermics.

Conventionally, the top of a well is first drilled to a relatively smalldepth of several tens of metres by means of a large-diameter tool, forexample of about 500 mm wide, and is lined with a string of tubes ofthis diameter. The drilling diameter then decreases by steps until thebottom of the well, which may be drilled with a substantially smallerdiameter of about 150 mm in the same example. Such a well is then casedwith plural strings of concentric tubes, each lowered at the end ofdrilling at the corresponding diameter and all suspended from thesurface; the tubes of largest diameter extend from the surface toseveral tens of metres deep, and the tubes of the smallest diameterextend from the surface to the bottom of the well, whose depth may reachseveral thousand metres. The space between the casings and the earth isfilled with cement for example.

After the well has been completely drilled and lined, a string oftubings can be lowered in order to allow in particular the rising ofhydrocarbons to the surface, i.e. actual working of the well. Obviouslythis string of tubings has an outer diameter which is slightly smallerthan the inner diameter of the string of casings.

To equip a well therefore leads to the installation of a large number oftubes of various dimensions, usually connected by means of threadedjoints taking into account the advantages of this type of connection. Itis desired to make these tubes as slim as possible in order to avoid toolarge diameters of casings near the surface. In fact keeping within therequirements and specifications applicable to threaded joints oftenleads to their having a larger thickness than that of the current partof the tubes, and this makes it imperative to increase the diametricprogression between concentric strings when descending deep down intothe well.

The connecting together of tubes is effected either by screwing thethreaded ends of the tubes into one another (known as integral joints),or by means of threaded couplings covering their ends. The tubes arelowered consecutively after being screwed into the end of the precedingtube or coupling.

The specification API 5 CT of the American Petroleum Institute (API)thus defines tubular threaded joints between two large-length tubes(“integral-joint tubing”, “extreme-line casing”), as well as coupledthreaded connections comprising two threaded joints for assembling twolarge-length tubes by means of a coupling. These API joints are onlymade sealing-tight by the application of a grease charged with metalparticles, which fills the gaps between threads.

Obviously the links between tubes (or between tubes and couplings) mustremain sealing-tight whatever the loads to which the tubes are subjectedduring their descent into the well, and within a wide range of weightsupported, since each joint supports at least in part the tubes locatedabove itself. Furthermore, the mechanical performance of the threadedjoints seem to be closely linked to their geometric characteristics.

A threaded joint is first defined by an “efficiency” under tension,determined by the ratio between the cross-section of the tube at thethread and the cross-section of the tube along its length.

Furthermore, when the pressure of the internal or external fluid exertedon the tubes becomes excessive, the threads may disengage, especiallywhere the threadings have rounded triangular threads. This is why it isgenerally preferred to implement trapezoidal threads.

This being the case, whatever the type of thread used, there is always,in spite of the use of grease charged with particles, a leak channelinto which a fluid under high pressure can circulate due to the playbetween the non-contacting surfaces. For a tensile load, there is afluid pressure threshold beyond which the combined tension and pressureload causes the API threaded joints to disengage or jump out at thecontacting threads of the male and female parts.

Threaded joints and connections have to this end been the subject ofvarious improvements: for example, the patents FR 1489013, EP 0488912,and U.S. Pat. No. 4,494,777 have aimed to create what are known assuperior or ‘premium’ tubular threaded joints which are particularlysealing-tight by virtue of metal-to-metal sealing bearing surfaces andof judiciously disposed stops between male and female elements.

This can be effected by two tapering sealing surfaces in interferingcontact, the male sealing surface being disposed outwardly beyond themale thread and the female sealing surface being disposedcorrespondingly over the female element. Transversely located stopsurfaces are used in cooperation to position the sealing surfaces and toincrease their efficiency.

As indicated, after lowering of a tubular string into a well, it isintended to subject this to diametric expansion with permanent plasticdeformation. This is effected for example by means of a ball which isforced to pass inside the string: see patents or patent applications WO93/25799, WO 98/00626, WO 99/06670, WO 99/35368, WO 00/61915, GB2344606, GB 2348657. This offers the following advantages:

-   -   lowering a string of low bulk, which is then forcibly expanded;    -   thus installing a string of casings,    -   in the same manner, sealing in situ the holes of a casing or        tubing pierced by corrosion or friction with the drilling rods,        or even of lowering into the well low-bulk tubes which will be        expanded to the desired diameter once in place,    -   finally and above all, permitting the drilling of well bores of        a uniform diameter over their entire length, whose casing is        realised by a string of tubes all of the same diameter, the        tubes being inserted in the non-expanded state, then being        expanded in situ to the diameter of the well bore.

It would therefore be possible to substantially decrease the number oftubes necessary to equip a well by eliminating the larger-diameter tubeshaving a greater thickness. The cost of the well is consequentlyreduced. It is even conceivable to drill the well directly with thestring of casings, which would act as a guide for the drilling rods.

It has been found that realising threaded joints which retain theirperformance after this expansion is extremely difficult, especially asthis must be reliable (all the joints must hold) and stable in operatingconditions.

It has been found that the conventional tubular threaded joints such asthose according to the patent U.S. Pat. No. 4,494,777 do not withstandplastic diametric expansion. After expansion on these joints, thefollowing is found:

-   -   an absence of sealing-tightness (which in addition makes it        impossible to effect expansion by pushing the ball hydraulically        through the string);    -   a deflection of the male end towards the inside of the joint        inducing an internal projection into the space defined by the        inner functional diameter, which considerably reduces in an        unacceptable manner the inner functional diameter of the string;    -   possible rupture of the lip of the male end by exceeding the        capacity for deformation of certain regions which are        particularly stressed due to the variations in thickness along        the length of male and female elements relative to the thickness        in the body of the tube.

It has therefore been tried to form a tubular threaded joint which iscapable of withstanding the expansion operation in the well and which issealing-tight to liquids and to gases after the expansion operation. Ithas also been tried to make the tubular threaded joint simple andeconomical to produce. It has further been tried to give the threadedjoint excellent metallurgical properties during operation thereforeafter expansion, in particular in that it has in this state a sufficientyield strength that it is free of brittleness and that it has goodresistance to sulphide stress cracking.

Threaded joints are known having a male lip corresponding to a femalehousing (U.S. Pat. Nos. 4,611,838, 3,870,351, WO 99/08034, U.S. Pat. No.6,047,997). It has been found that these known assemblies have nosealing-tightness after plastic expansion, but in any case this is in noway intended.

In U.S. Pat. No. 4,611,838, the male lip has a male end annular surfacehaving an annular tooth; a female shoulder annular surface comprising anannular groove is provided. For abutment, the male lip has a toroidalouter peripheral surface and the female housing has a conical innerperipheral surface. These peripheral surfaces interfere radially at theend of screwing together in order to form sealing areas. U.S. Pat. No.4,611,838 aims to maximise the radial interference of the toroidal outerperipheral surface of the male lip with the conical inner peripheralsurface of the female housing at the end of screwing together (andthereby sealing-tightness of the threaded joint) by virtue of the shapeof these peripheral surfaces and the supporting effect of the lowersurface of the groove to the lower surface of the tooth. But the maleend surface according to U.S. Pat. No. 4,611,838 is not well held inposition in the end surface of the female shoulder of the threaded jointand therefore does not permit the transmission of a bending moment tothe free end of the male lip due to the free space between the upperwall of the tongue at the free end thereof and the upper wall of thegroove at the bottom thereof. Sealing-tightness after expansion cannottherefore be guaranteed.

U.S. Pat. No. 3,870,351 has a configuration of the male lip and end andof the female housing close to the configuration of the patent U.S. Pat.No. 4,611,838, the male free end surface being convexly curved andbearing on a concavely curved female shoulder surface so as to form twosets of metal-to-metal sealing surfaces, one at the curved surfaces, theother set being disposed on the outer peripheral surface of the male lipand on the inner peripheral surface of the female housing. Such aconfiguration makes it possible to increase the radial interferencebetween the peripheral sealing areas on the screwed joint, which is nothowever sufficient for the application under consideration(sealing-tightness after expansion).

WO 99/08034 describes a threaded joint with square turns having a malelip corresponding to a female housing and having male end annularsurfaces and female shoulder annular surfaces in the form of abuttingrebates fitting one in another. The outer peripheral surface of the malelip and the inner peripheral surface of the female housing havecylindrical parts which interfere radially with one another in order toform a set of peripheral sealing areas at the end of screwing togetherwhen the male and female rebates are fitted together. The configurationof these surfaces is complex and expensive to realise, and gives noguarantee of sealing-tightness after plastic expansion. Furthermore, thetrapping of grease may lead to poor positioning of the threadedelements.

Finally, U.S. Pat. No. 6,047,997 describes a structure of drilling rodsfor underground pipes for which there is no particular demand forsealing-tightness. The male end face according to this patent is rebatedin a female shoulder face, but the figures show a considerable gapbetween the outer peripheral surface of the male lip and the innerperipheral surface of the female housing. This is not satisfactoryeither for the application under consideration.

In the connecting technique by expansion, each tube is placed end-to-endwith the tubes already assembled after passing through the tubespreceding it. In order to allow the tube to pass through, the diameterof each tube already assembled will have undergone expansion of about 10to 25%, starting with the first tube, by the passage of a ball ofgenerally conical shape pulled from the surface of the well. Thisexpansion of the tubes also makes it possible to improvesealing-tightness at the contacting surfaces of the joints.

An embodiment of a metal-to-metal sealing joint in the form of a fingeradapted to this technology is disclosed in WO 02/01102 cited above.Another embodiment is shown in the not-yet-published French Patent FR 0200055 cited above. Each of these embodiments describes a sealing-tightjoint capable of being expanded and, once expanded, having sealingregions which ensure sealing-tightness to liquids, and even gas.

A sealing region is formed of two surfaces in contact subjected tocontact pressures. One sealing region remains sealing-tight to liquidpressures, or gas pressures, which are even greater the since thecontact pressure on these surfaces is strong. Moreover, the dimensionsof these sealing surfaces (width and length) also have an effect onsealing-tightness. The invention proposes to improve thesealing-tightness of these joints at liquid and gas pressures inparticular by increasing the contact pressure level with the sealingregions.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 shows a joint comprising a male threaded element 1 disposed atthe end of a first tube 11. This male element is screwed in abutmentinto a threaded female element 2 disposed at the end of a second tube.The inner diameter of the male threaded element is in this case equal tothe inner diameter DI of the tubes 11, 12. In the embodiment in FIG. 1,the outer diameter of the female threaded element is equal to the outerdiameter DE of the tubes 11, 12 only by way of example.

The joint in FIG. 1 is shown in the state of being simply screwed intoabutment before any diametric expansion operation.

The second tube 12 as shown is a great-length tube. This second tubecould be, in a manner not shown, a coupling equipped on one side withthe female element 2 and on the other side with a second female elementwhich may or may not be symmetrical to the latter and which is screwedto a male element located at the end of another great-length tube.

Only the male element 1 is shown in FIG. 2.

It comprises a male thread 3, which is tapered with trapezoid thread andextends to its free end by a non-threaded end part formed by a groove 21and by a lip 5 and ends with an annular male end surface 9.

The groove 21 has a shallow U-shape.

It starts immediately beyond the thread and its depth h_(g) is smallerthan the height of the thread 3. Thus the bottom of the groove meets theroot of the first thread.

The width of the groove I_(g) is substantially equal to 4 times itsdepth h_(g).

The lip 5 has:

-   a) an outer peripheral surface 7 of cylindrical form,-   b) an inner peripheral surface 19 which corresponds to the end    region of the cylindrical inner peripheral surface of the first tube    11.

The lip 5 therefore has a uniform thickness e_(l) substantially equal tohalf the thickness e_(t) of the tube 11. It has a length l_(t) measuredfrom the end of the groove to the perpendicular of the surface 15(defined below) substantially equal to 3 times the lip thickness e_(l).

The male end surface 9 forms a rebate. This rebate is formed of a maleannular transverse surface 15 and an annular tongue 13 projectingaxially, adjacent to the transverse surface 15. The male transversesurface 15 is located on the side of the rebate oriented towards theinterior of the threaded joint.

The outer peripheral surface of the tongue 13 is an extension of theface 7 of the lip, whereas its inner peripheral surface 17 iscylindrical for example.

The radial thickness of the tongue 13 is substantially identical to thatof the transverse surface 15, whereas the height of the tongue (or axialprojection thereof) is substantially equal to the radial thickness ofthe tongue. It may also be equal to 1.5 times this radial thickness inorder better to retain the free end of the tongue during expansion.

The female element 2 is shown alone in FIG. 3.

It comprises, from the free end of the female element, a female thread 4with trapezoidal threads homologous to the male thread 3, then anon-threaded part 6. This non-threaded part 6 forms a housing tocorrespond to and cooperate with the lip 5 of the male element 1.

The female housing 6 has a peripheral surface 8 turned inwards, ofcylindrical shape, connected on one side to the female thread 4 and onthe other side via a female shoulder 10 to the inner cylindricalperipheral surface 20 of the second tube 12.

In general, the diameter of the peripheral surface 8 of the housing isvery slightly larger than the diameter of the outer peripheral surface 7of the male lip 5. Thus the faces 7 and 8 can slide into one anotherwith little clearance during screwing of the male element into thefemale element, e.g. with a clearance of 0.2 mm. The advantage of suchsliding will be explained below.

The female shoulder has an annular shoulder face 10 which is disposedsubstantially correspondingly and which has a shape substantiallysimilar to that of the male end 9. The face 10 forms a rebate consistingof a female transverse annular surface 16 and an annular groove 14adjacent to the transverse surface 16.

The female transverse surface 16 is located on the side of the rebateoriented to the interior of the threaded joint.

The wall 18 of the groove 14 adjacent to the transverse surface 16 iscylindrical for example and can join thereto by a chamfer or roundededge. The opposite wall of the groove is an extension of the peripheralsurface 8. During screwing together of the threaded joint, the surface17 of the tongue ‘rises’ over the wall 18 of the groove until the freetransverse end of the tongue extends against the bottom 24 of the groove14. The axial height h_(r) of the tongue 14 and the axial depth P_(r) ofthe groove are such that the transverse surfaces 15 and 16 do not comeinto contact until after further screwing. The small clearance betweenthe cylindrical surfaces 7 and 8 and between the surfaces of the tongueand the groove which are an extension of them therefore permitsevacuation of the grease at the end of screwing and therefore correctpositioning of the lip 5 relative to the housing 6.

FIGS. 4 to 7 illustrate the deformation phenomena produced whendiametric expansion of about 15% is realised by means of a ball on thetubes connected by the threaded joints which have just been describedand which ultimately permit a sealing-tight expanded joint.

Such deformation carried out on metal materials leads to plasticdeformation of the metal.

Thus for example one passes from an outer diameter of 139.7 mm (5.5 in)on the second tube 12 upstream of expansion, and consequently in thepart not yet deformed, to an outer diameter of 157.5 mm (6.2 in) on thefirst tube 11 expanded (at the level of or downstream of the exit cone33 of the ball). It is therefore imperative to use for the tubes a metalwhich allows such plastic deformation.

The plastic deformation generated increases the yield strength of theproducts: a tube having initially an elastic limit of 310 MPa (45 KSI)will have thus increased to 380 MPa (55 KSI) after deformation.

The diametric expansion is carried out in a known manner by means of aball 30 (FIG. 4) of adequate maximum diameter. The ball is forcedthrough the tubes either by pulling with the aid of drill rods or bypushing by hydraulic pressure, for example.

The ball has for example a biconical shape with an entry cone 31 onwhich the expansion is carried out, a middle cylindrical part 32 and anexit conical part 33. All the surfaces of the parts of the ball arejoined together by adapted connection radii.

WO 93/25800 discloses in particular angles of entry cones especiallyadapted to the diametric expansion of tubes known as EST (expandableslotted tubing) for the working of hydrocarbon wells.

Since the tubes 11, 12 have a substantially constant cross-section,their ends do not create a particular problem during passage of theball, provided that the capacity for deformation of the metal of whichthey are made is sufficient.

The process of expansion of the threaded joint can be broken down into 4phases which are the subject of FIGS. 4 to 7.

Although the expansion operation can be carried out entirely in thereverse direction and lead to adequate results, the preferred mode ofdeformation has been shown in which the ball moves from the male element1 of the first tube 11 to the female element 2 of the second tube 12.

a) Expansion Phase on the Ball Cone

FIG. 4 shows the threaded joint during this phase.

The expansion is carried out by the entry cone 31 of the ball 30 andFIG. 4 shows the male 3 and female threads 4 during diametric expansion.

In FIG. 4, the entry cone 31 of the ball 30 starts the deformation ofthe male lip and of the homologous female housing region by bending themin order to incline them relative to the axis of the connection.

During this expansion phase, the reaction loads to the passage of theball 30 are progressively transferred from the first tube 11 to thesecond tube 12.

Due to these reaction loads, the male lip 5 is compressed axially duringthis expansion phase by the annular face of the female shoulder 10.

The end of the expansion phase corresponds to the arrival of the freeend of the male element at the end of the entry cone 31 of the ball.

b) Bending Phase

During this phase, the male lip is located level with the central part32 of the ball: see FIG. 5.

i) Male Lip

The male lip 5 is subjected at both ends to bending moments in oppositedirections.

The male end surface 9 is in fact kept in position in the femaleshoulder face 10 due to the rebates with bearing surfaces 15, 16 and tothe embedding device of the tongue 13/groove 14.

The embedding of the rebates forces the free end region of the male lip5 to follow the inclination of the region 22 of full thickness of thefemale element beyond the shoulder. This region 22 is again in theprocess of expansion on the entry cone 31 of the ball and thereforecreates a bending moment at this level.

The other end of the lip, on the side of the male thread 3, is no longersupported and on the contrary imposes on the lip a bending momentopposite to that at the free end of the lip.

The bending moments of opposite sign at the two ends of the male lipbring about a banana-shaped curvature of the male lip 5, as in FIG. 5,whilst the outer peripheral surface 7 of the lip 5 takes on a curvedconvex shape.

The state of axial compression of the male lip 5 at the end of the phaseof expansion facilitates its curvature under the effect of the bendingmoments.

The groove 21 located between the male lip 5 and the male thread 3 actsas a plastic pivot which accentuates the curvature of the male lip bylimiting the width over which this curvature can take place.

It should be watched in this case, however, that the axial compressionstresses on the male lip do not bring about buckling of the metal 23under the groove. This buckling would be converted into a projection ofthe metal under the groove relative to the inner peripheral surface 19.

ii) Female Housing

The same bending phenomenon is produced on the female housing.

The region 22 of full thickness which is relatively rigid compared tothe relatively slim regions of the lip undergoes additional expansionupon passage of the middle part, such that the inner diameter of theregion 22 becomes larger than that of the middle zone 32 of the ball.The additional expansion phenomenon is described in the specification WO93/25800.

c) Straightening Phase

This phase illustrated in FIG. 6 corresponds to the passage of thefemale region 22 of full thickness over the middle part 32 of the ball30.

i) Female Housing

The bending generated in the preceding phase tends to be brought back tozero under the effect of tension and circumferential stresses, whichgenerates a state of inverse axial bending stresses relative to thecurvature, thus bringing about straightening.

The bending moment generated by these stresses is proportional to thethickness of the material upstream of the straightening. At the momentof arriving on the tube 12 of full thickness (region 22), the bendingmoment is not sufficient to straighten the inner peripheral region ofthe female housing, which then tends to dive-towards the axis of theproduct. This behaviour is manifested by a local reduction of outerdiameter of the tube 12.

ii) Male Lip

During the straightening of the female part, the difference in axialbulk which was generated by bending decreases. The male lip 5 thereforeprogressively loses the state in which it was under compression. This isfollowed by separation of the surfaces 15, 16 initially abutting. Thisphenomenon is reinforced by ‘the diver’ of the inner peripheral face 8of the female housing which produces an effect of opening of theabutments 15, 16.

The banana-shaped deformation imposed in the preceding phase isconserved.

d) Final State

FIG. 7 shows the final state of the threaded joint after passage of theball.

The state of hoop stresses generated by expansion leads to shrinking ofthe inner surface 8 of the female housing on to the outer peripheralsurface 7 of the male lip. One can therefore refer to self-shrinking ofthe surfaces 7, 8 of the threaded joint in the expanded state, whichensures sealing-tightness. The male lip 5 does not dive towards theaxis, as the radial offset imposed by the embedding of the rebates 9, 10has generated sufficient plastic deformation.

The springback displacement of the elements of the threaded joint afterpassage of the ball is negligible compared to the plastic deformationbrought about.

The radial shrink-fitting induces a contact pressure of several tens ofMPa, even more than 100 MPa, sufficient to ensure sealing-tightness atthe internal or external pressures at the threaded joint. The length ofshrink-fitting is sufficient over the entire circumference of thecontact surfaces to ensure stable sealing-tightness between thesecontact surfaces.

Sealing-tightness is further necessary when expansion is carried out bypushing the ball 30 hydraulically under a pressure of 10 to 30 MPa, andany leak at the joints that have already been expanded prevents the ballfrom penetrating further forward in the string and consequently blockingthe process of expansion.

Too much clearance between the peripheral face 7 of the male lip 5 andthe peripheral face 8 of the female housing on the threaded joint beforeexpansion would not allow the shrink-fitting of these surfaces at theend of the expansion operation.

Radial interference between these surfaces in the initial state beforeexpansion is liable to hinder the differential deformation (curvature,straightening) between these surfaces during expansion operations, whichdifferential deformation makes it possible to effect shrink-fitting ofthese surfaces at the end of the expansion operation. It may also leadto galling of these surfaces during screwing together and poorpositioning of the elements with incorrect embedding of the faces 9 and10, and consequently to poor shrink-fitting of the surfaces 7 and 8after expansion.

In a preferred embodiment, the form with an annular rebate withtransverse surfaces 15, 16 and the tongue 13/groove 14 mechanism makesit possible to prevent diving of the male free end during expansion.Other embodiments of encased surfaces 9, 10 are possible in order togive the same result.

A too-small male lip 5 of thickness e_(l) smaller than one third of thethickness e_(t) of the tubes 11, 12 does not make for an effectiveabutment with the transverse surfaces 15, 16.

If the thickness e_(l) of the male lip 5 is on the other hand largerthan ⅔ of the thickness e_(t) of the tubes 11, 12, the thickness of thetube 12 at the level of the female housing brings about a criticalcross-section for the female thread 4 which is too weak and consequentlyoffers insufficient resistance to tension of the threads.

The ratio of length/thickness of the male lip 5 dictates the behaviourunder compression and bending of the lip 5.

A male lip 5 of length I_(l) smaller than its thickness does not givesufficient bending of the peripheral surface 7 of the male lip 5 and/orstraightening of the peripheral surface 8 of the female housing.

A male lip 5 of length I_(l) larger than 4 times its thickness e_(l) cancause buckling of the male lip and an internal projection thereof on theside of the thread.

This effect is accentuated by the presence of a groove 21 between themale thread 3 and the male lip 5.

This is why the groove preferably has a depth limited to thread heightand a length which is limited relative to its depth.

A tongue 13 of insufficient radial thickness and axial height lower thanthe radial thickness could not be supported sufficiently duringexpansion.

We refer now to FIG. 8, showing a tubular joint after screwing togetherof the partly threaded tubular elements, which joint is intended to beexpanded diametrically according to the invention.

This joint has male 11 and female 12 tubular elements as shown inFIG. 1. The end part of the male tube has the lip 5, whose peripheralsurface 8 is capable of coming into contact with the peripheral surface7 of the female housing 8 of the female tube 12 upon expansion of thejoint. The contact region with contact pressure between the surfaces 7and 8 after expansion is known as the inner sealing region CI, as it islocated towards the interior of the joint. After expansion, there isalso a contact region between a surface of the tongue of the male lipand an opposite surface of the groove of the female tubular element.

A tubular sleeve 36 is disposed concentrically to the female tubularelement 12. This tubular sleeve 36 has an inner diameter such that itallows this tubular sleeve to be threaded by an operator, beforescrewing of the tubular elements 11 and 12, on to the female tubularelement 12 and to be in contact with the outer surface 37 of the tubularelement 12. This tubular sleeve extends over all its length lm1 in orderto overlap the lip 5 axially and to extend beyond the lip 5 on eitherside, i.e. on the side of the thread and beyond the tongue 13. Thetubular sleeve 36 is advantageously centred on the lip.

At the end of screwing together and before expansion, the tongue 13 isaxially abutting against the bottom of the groove 14 and the sealingsurfaces 7 and 8 are cylindrical and disposed with slight clearance fromone another at the end of screwing together. The lip 5 is held duringexpansion by the embedding device of the tongue 13 and groove 14.

In the example, the tubular sleeve 36 is formed of material identical tothat of the tubular elements whose yield strength is for exampleidentical to the yield strength of the material of these tubularelements. After diametric expansion, the tubular sleeve generates aresilient springback force, which is added to that of the female elementand counteracts the springback force of the male element. Theshrink-fitting of the tubular sleeve over the female element is thuseffected. Moreover the difference of springback force between the maleelement on the one hand and the assembly consisting of the sleeve andfemale element on the other brings about compression of the femaleelement. As the tubular sleeve 36 overlaps the surfaces 7 and 8 andslightly beyond, the compression is translated into an increase incontact pressure between the sealing faces 7 and 8 of the male andfemale elements. The shrink-fitting of the female element over the maleelement is thus effected. The presence of the tubular sleeve 36 requiresan expansion energy scarcely larger than when there is no tubular sleeve(of about 10%) and considerably reinforces the contact pressure at theinner sealing region CI after expansion (of about 200% for a sleeve of athickness of 4 to 5 mm).

In the embodiment shown, before expansion, the tubular sleeve 36 isdefined by

-   -   a length of overlap lm1 roughly equal to at least the length of        the lip 1 with the addition of a length of about 2 to 8 times at        most the width of a turn of the thread,    -   a radial thickness em1 limited between a maximum radial        thickness specified by the maximum bulk of the joint and a        minimum radial thickness specified by too weak an effect of the        sleeve on the springback force of the threaded elements:        advantageously, the radial thickness is about a few millimetres,        e.g. at least 1.5 mm and preferably about 4 to 5 mm for tubes of        an outer diameter of 150 mm and a thickness of 7 to 8 mm. The        preferred thickness of the sleeve is substantially close to that        of the male lip. After expansion the radial thickness is at        least equal to 1 mm.

In one embodiment of the invention, the surfaces 7 and 8 define what isknown as the inner sealing region CI of the joint after diametricexpansion. However, another sealing region is formed before and afterdiametric expansion of the sealing-tight joint shown in FIG. 8.

Thus the female tubular element 12 has, between its thread and its freeend, a non-threaded female lip 38. This female lip 38 has an innerperipheral face 41 ending with a radial surface 39 forming an annularsurface. The male tubular element 11 has an outer peripheral surface 40on the side of the male thread opposite to its free end. After screwingtogether fully the male and female tubular elements, the innerperipheral surface 41 interferes radially with the outer peripheral face40 of the male tubular element 11 so as to define a sealing-tight regionbefore expansion. The surfaces 40 and 41 are both conical and of similarconicity. During expansion, the female lip not in axial abutment againstthe male element, there are no signs of bending or counter-bending as inthe case of the male lip in axial abutment against the female element.Thus the female lip does not dive towards the axis. After expansion,there happens just a springback replacement of the lip 38 which isslightly greater than that of the subjacent male element. This bringsabout sealing-tight contact between the inner peripheral surface 41 ofthe female lip and the corresponding peripheral surface 40 of the maletubular element 11. The interference of the surfaces 40 and 41 afterscrewing together ensures contact between these surfaces upon springbackat the end of after expansion.

The sealing-tight contact region between the surfaces 40 and 41 afterexpansion is known as the outer sealing-tight region CE, since it islocated towards the outside of the joint.

Apart from any other means, the external sealing-tightness created atthe region CE is however less than that created at the region CI.

A tubular sleeve 34 is disposed concentrically to the female tubularelement 12. This tubular sleeve 34 has an inner diameter such that itallows the tubular sleeve to be threaded on by an operator beforescrewing of the tubular elements 11 and 12 on to the female tubularelement 12 and to be in contact with the outer surface 37 of the tubularelement 12. This second tubular sleeve extends over its entire lengthlm2 in order to overlap axially the peripheral surfaces 40 and 41capable of defining the sealing-tight region before and after expansionand to extend beyond these faces on either side, i.e. on the side of thethread and beyond the radial surface 39. In the example, the tubularsleeve 34 is formed from a material similar to that of the tubularelements and whose yield strength is for example equal to the yieldstrength of the material of these tubular elements. After diametricexpansion, the tubular sleeve generates a springback force which isadded to that of the female element in order to counteract the resilientrestoring force of the male element. The shrink-fitting of the tubularsleeve over the female element is thus effected. Moreover, thedifference in springback between the sleeve and the inner surface of themale element brings about compression of the female element. As thetubular sleeve 34 overlaps the surfaces 40 and 41 and slightly beyond,compression is translated into an increase in the contact pressurebetween the sealing surfaces 40 and 41 of the male and female elementsrelative to a similar joint without a sleeve 34. The shrink-fitting ofthe female element over the male element is also effected. The presenceof the tubular sleeve 34 requires an expansion energy scarcely anygreater than without a tubular sleeve and considerably increases thecontact pressure at the outer sealing-tight region CE after expansion(of more than about 300%).

In the embodiment shown, before expansion, the tubular sleeve 34 isdefined by

-   -   a length of overlap lm2 roughly equal to the axial length of the        female lip 38 with the addition of a length of about 2 to 8        times at most the width of a thread,    -   a thickness em2 limited between a maximum thickness specified by        the maximum bulk of the joint and a minimum thickness specified        by too weak an effect on the springback: advantageously, the        thickness is about a few millimetres, e.g. at least 1.5 mm and        preferably 4 to 5 mm for tubes with an outer diameter of about        150 mm and of a thickness of 7 to 8 mm. Here also, the thickness        of the sleeve 34 is preferably about the same size as that of        the female lip. After expansion, the radial thickness is at        least equal to 1 mm.

Whether for the sleeve 34 or the sleeve 36, it has been found that ashort sleeve, discontinuous in material from the male and femalethreaded elements, would improve the sealing-tightness performance, inparticular of external sealing-tightness, much more than a long addedsleeve or than a simple extra thickness of the material on the femaleelement instead of the sleeve or sleeves. Such a teaching would notappear to be absolutely obvious.

Various methods of mounting sleeves are conceivable.

In one embodiment, the tubular sleeve 34 has a radial projection 42 atone end. Thus, before screwing together of the tubular elements 11 and12, an operator threads the tubular sleeve 34 on to the tubular elements12 from the end opposite to that having the projection, the innerperipheral surface of the sleeve being in contact with the outerperipheral surface 37. The tubular sleeve 34 is threaded on until theradial projection 42 comes into contact with the radial surface 39. Thetubular sleeve 34 is thus positioned axially. The radial projection 42may advantageously be adhered to the radial surface 39 so as to improvethe contact pressure. A “grease glue” can be used, which hardens in afew minutes in anaerobic conditions and makes it possible to hold theposition of the tubular sleeve relative to the female element duringexpansion. The layer of glue can be sheared and cracked during expansionwithout posing a risk.

In a modified embodiment, the tubular sleeve 36 and/or 34 is (are)threaded over the tubular element 12 before screwing together by anoperator, then positioned axially by means of the presence of marking onthe outer peripheral surface 37 of the female tubular element 12, inwhich case the marking may be a shallow groove 47. The axial position ofthe tubular sleeve(s) 36 and/or 34 may be held by means of the “greaseglue” as in the case of the sleeve with a radial projection. The axialposition of the tubular sleeve(s) 36 and/or 34 may also be held by avery slight shrinking on to the female tubular element. Theshrink-fitting may be effected by heating of the sleeve and/or coolingof the female element.

The radial thickness of a tubular sleeve may be decreased at the expenseof decreased efficiency in the reinforcement of the sealing-tightnesscreated by the sleeve. However, it is possible for thin sleeves tocompensate somewhat for their loss of efficiency by increasing theiryield strength relative to that of the male and female elements 11 and12. The higher the yield strength of the sleeve compared to the yieldstrength of the male and female elements, the better thesealing-tightness at a given thickness. The yield strength of thetubular sleeve is capable of being modified by heat treatment. However,the ductility of the material is generally reduced by the increase inyield strength. A compromise can be found between ductility, which mustbe sufficient to generate diametric expansion without rupturing thetubular sleeve, and a yield strength sufficiently high to ensuresufficient sealing-tightness properties in spite of the restrictedradial thickness of the tubular sleeve.

If a tubular element only has one outer CE or inner CI sealing-tightregion, this sealing-tight region is capable of ensuring thesealing-tightness against fluids passing from the inside to the outsideas well as from the outside to the inside. In this case, the terms“outer sealing-tight region” and “inner sealing-tight region” make itpossible substantially to locate the sealing-tight region at the freeend of the male or female tubular element.

In annexe I, the relative properties of threaded joints are shown asintegrated contact pressure over the width of contact. This study aimsto compare, relative to a simple reference threaded joint (case 1) thevarious embodiments according to the invention adapted to this simplethreaded joint. The joint taken as a reference is a threaded joint withan outer diameter of 152.4 mm (6 inches) and a metric weight of 27.8kg/m (18.6 lb/ft) in AISI 420 (13% Cr) steel according to the Americanstandard (corresponds to the European standard X20Cr13) treated for thegrade API L80 (API=American Petroleum Institute) corresponding to theminimum yield strength of 551 MPa.

The tables 1 and 2 relate respectively to the results of external andinternal sealing-tightness as a percentage for each case consideredcompared to the internal sealing-tightness of the reference case:

-   -   case 1: reference threaded joint,    -   case 2: reference threaded joint covered by a very long sleeve        fixed to the male threaded element and overlapping the thread        and the male and female lips, of thickness 4.5 mm, in steel        identical to that of the threaded joint (13% Cr) and treated        identically to the joint (API L80)    -   case 3: reference threaded joint equipped with two short sleeves        according to the present invention (FIG. 8) of the same        thickness, material and treatment as in the preceding case,    -   case 4: the same as case 3, but having a single sleeve disposed        at the level of the female lip, being very thin (thickness        1.6 mm) and adhered to the female element at the level of its        radial projection,    -   case 5: the same as case 4, but having a sleeve treated for a        grade API P110 (corresponding to the elastic limit R_(p 0.2)≧758        MPa).

In case 1, the internal sealing-tightness is excellent but the externalsealing-tightness is weaker (44% of the internal sealing-tightness). Along sleeve (case 2) only improves the internal sealing-tightness. Theuse of two short sleeves (case 3) of similar thickness to case 2improves both the external and internal sealing-tightness. By severelydecreasing the thickness (case 4), it is possible to retain sufficientexternal sealing-tightness (only one studied). By increasing the gradeof the sleeve, and therefore the yield strength (case 5), it is possibleto increase the external sealing-tightness, which virtually reaches thelevel of sealing-tightness of the reference case.

The peak of effort (not shown here) generated by the presence of thesleeve for diametric expansion and the expansion energy is very limited.

For a tubular element having the two inner and outer sealing-tightregions, a modified embodiment of the tubular sleeve consists in atubular overlapping piece 45 as shown in FIG. 11, comprising the sleeves34 and 36 of FIG. 8 connected together by a tubular brace 46. Thistubular brace 46 is of much smaller radial thickness than that of thesleeves 34 and 36 so as virtually not to oppose the diametric expansionforce over the entire length of the brace 46.

The various methods of assembling this overlapping piece are the same asfor the tubular sleeve 34 on its own.

The invention is not limited to the embodiments described by way ofexample.

The invention applies either to joints having only the internalsealing-tight region or the joints having only the externalsealing-tight region, or joints having both sealing-tight regions. Theinvention can be adapted to joints having other sealing-tight regionssuch as intermediate sealing-tight regions for example.

Annexe I

TABLE 1 Case number 1 2 3 4 5 External sealing-tightness 44 45 158 89 99(in % compared to internal sealing-tightness of case 1)

TABLE 2 Case number 1 2 3 Internal sealing-tightness (in % 100 220 201compared to internal sealing- tightness of case 1)

1. An expandable threaded tubular joint comprising: a first tubularelement and a second tubular element, the first and second tubularelements having respective mating threads, the first and second tubularelements having respective first and second non-threaded lips extendingbetween their threads and respective free ends, wherein each of thefirst and second non-threaded lips of the first and second tubularelements comprises a respective first and second sealing surface, thetubular joint having a first state in which the first and second tubularelements are made up together by screwing together the mating threads,and the tubular joint having a second state, derivable from the firststate by a diametric expansion to a predetermined extent, in whichsecond state each sealing surface comes in sealing-tight contact with anopposite surface of the other tubular element, wherein the tubular jointhas first and second tubular sleeves having an inner diameter fittingover the second tubular element before screwing together the first andsecond tubular elements, the first sleeve being positioned in order toextend axially substantially opposite to the first non-threaded lip andthe second sleeve to be positioned in order to extend axially oppositeto the second non-threaded lip, the fitting in the first state beingsuch that the tubular sleeves effect at least shrink-fitting directly onthe second tubular element in the second state, thereby generating, inthe second state, a tubular sleeve springback force which cumulates witha springback force of the second tubular element for counteracting aspringback force of the first tubular element, and wherein the twosleeves are connected together by a brace, the sleeves and the bracebeing formed in one piece.
 2. The tubular joint according to claim 1,wherein the non-threaded lip of the first tubular element has a tongueat the end to engage in an axial abutment in a corresponding groove ofthe second tubular element after screwing together and before expansion,the non-threaded lip to be held by the tongue in the groove duringdiametric expansion.
 3. The tubular joint according to claim 1, whereinthe second sealing surface and a respective opposite surface interfereradially one with another in the first state.
 4. The tubular jointaccording to claim 1, wherein the first sealing surface and a respectiveopposite surface are disposed with a clearance fit from one another inthe first state.
 5. The tubular joint according to claim 4, wherein thefirst sealing surface and the opposite surface are cylindrical.
 6. Thetubular joint according to claim 1, wherein the brace is a tubular bracethat has at least one of a radial thickness smaller than that of thesleeves and a cross-section smaller than that of the sleeves.
 7. Thetubular joint according to claim 1, wherein the second tubular sleevehas a radial projection that comes into contact with a radial surfacedisposed at the end of the second tubular element to facilitatepositioning of the tubular sleeves.
 8. The tubular joint according toclaim 1, wherein the tubular sleeves are positioned axially on thesecond tubular element by shrink-fitting at least by cooling of thesecond tubular element.
 9. The tubular joint according to claim 1,wherein the tubular sleeves are positioned axially on the second tubularelement by shrink-fitting at least by heating of the tubular sleeves.10. The tubular joint according to claim 1, wherein the second tubularelement has a mark which is disposed on an external peripheral surfaceand which is to facilitate positioning of the tubular sleeve.
 11. Thetubular joint according to claim 10, wherein the mark is a shallowgroove formed in the second tubular element.
 12. The tubular jointaccording to claim 1, wherein the tubular sleeve has a radial thicknessof at least 1.5 mm.
 13. The tubular joint according to claim 1, whereinthe tubular sleeve is made of a material that has a yield strengthhigher than a yield strength of a material from which the first andsecond tubular elements are made.
 14. The tubular joint according toclaim 1, wherein the tubular sleeve is made of a material having a yieldstrength that is adjusted by heat treatment.
 15. The tubular jointaccording to claim 1, wherein each tubular sleeve has an overlap lengthroughly equal to the length of the lip opposite.
 16. The tubular jointaccording to claim 15, wherein each tubular sleeve has an overlap lengthroughly equal to the length of the lip opposite with the addition of atmost 8 times a pitch of the threads.
 17. The tubular joint according toclaim 1, wherein each tubular sleeve is axially centered on therespective lip opposite.
 18. An expandable threaded tubular jointcomprising: a first tubular element and a second tubular element, thefirst and second tubular elements having respective mating threads, atleast one of the first and second tubular elements having a non-threadedlip which extends between its threads and a free end and is providedwith a sealing surface, the tubular joint having a first state in whichthe first and second tubular elements are made up together by screwingtogether the mating threads, and the tubular joint having a secondstate, derivable from the first state by a diametric expansion to apredetermined extent, in which second state the sealing surface on atleast one of the first and second tubular elements comes insealing-tight contact with an opposite surface of the other one of thefirst and second tubular elements, wherein the tubular joint has atubular sleeve fitting over the second tubular element in the firststate of the joint so as to extend axially substantially opposite thenon-threaded lip, the fitting in the first state being such that thetubular sleeve effects at least shrink-fitting over the second tubularelement in the second state, thereby generating, in the second state, atubular sleeve springback force which cumulates with a springback forceof the second tubular element for counteracting a springback force ofthe first tubular element, whereby the tubular sleeve is held inposition relative to the second tubular element by a glue to make atleast part of the surface of the second tubular element adhere to atleast part of the tubular sleeve surface.
 19. The tubular jointaccording to claim 18, wherein the tubular sleeve has an overlap lengthroughly equal to the length of the lip opposite with the addition of atmost 8 times a pitch of the threads.
 20. The tubualr joint according toclaim 18, wherein each tubular element has a respective non-threaded lipwith a sealing surface, and each tubular element has a tubular sleeve,one tubular sleeve being positioned in order to extend axiallysubstantially opposite to the first non-threaded lip of the firsttubular element and the other tubular sleeve being the tubular sleevethat is positioned in order to extend axially substantially opposite tothe second non-threaded lip of the second tubular element.